This invention relates to screens for screen printing machines particularly multiple print head screen printing machines used for colour printing garments.
Garments such as tee shirts are decorated using multi printing head, screen printing machines. The number of heads correspond to the number of colours to be printed. U.S. Pat. Nos. 3,795,189 (Jaffa) and 5,031,527 (Eppinger) disclose examples of the type of machines used in printing garments.
The garments are supported on a pallet, which in turn is supported, for registry with the printing head, on a pallet arm. The pallet is moved successively past the desired number of printing heads until the printing is complete. Each printing head incorporates a silk screen frame carrying the image and devices for applying the ink including a squeegee and drive for spreading the ink and transferring an image from the screen to a garment on the pallet. After each color is printed it is usual to flash cure the ink before applying the next color.
It is necessary to prepare each screen for each print head by determining such parameters as print speed, flood speed and position limits for the squeegee the ink colour and squeegee material to be used, the screen tension, the number of print passes required, the optimum flash period for curing the ink and the print head on the machine to which the screen should be attached.
This preparation time can be time consuming and is often carried out on a smaller test printing machine to avoid unnecessary down time of the production screen printer. However after the screen is prepared the data has to be entered at each print head or into a central controller as described in U.S. Pat. Nos. 5,787,805 and 5,592,877. This also takes time and adds to the down time of the machine when the screens are fitted and the screen printing machine is made ready for printing. Screens for multi print head screen printers have never had any means for carrying screen printing parameters and usually the job number and customer name was hand written on an unused portion of the screen or on the frame. In offset printing using cylindrical printing presses this problem has been partially addressed but in that environment the number of printing parameters is less.
U.S. Pat. No. 4,665,824 discloses the use of a removable job strip that can be read by a scanner to obtain printing control data for the printing controller.
U.S. Pat. No. 6,123,024 describes a printed circuit board screen printing stencil which carries one or more readable tags or transponders containing data relating to the stencil pattern to be printed, the solder paste viscosity, the temperature of application, the number of printed circuit boards printed and the total time of use of the stencil.
The printing of industrial printing of circuit boards and printing by rotary printing press are very different industries compared to silk screen printing of garments and the developments outlined above can not be used in garment screen printing machines.
It is an object of this invention to overcome these problems.
To this end the present invention provides a method of preparing a silk screen for use in a screen printing machine having an electronic controller which includes the steps of
1. fitting the screen to a test machine
2. determining the printing parameters applicable for that screen,
3. storing the parameters on a readable storage means on said screen
4. fitting the screen on said screen printing machine and
5. commencing the printing operation whereby the electronic controller reads the printing parameters on said readable storage device and actuates the print head in accordance with the stored parameters.
By incorporating an electronic storage means on the silk screen itself the need to rekey the data after the parameters have been selected is avoided. This not only saves time but avoids errors in rekeying and loss of the programs if the screen printing machine is defective and another machine is required.
In another aspect this invention provides a system for preparing a screen for a multi print head garment screen printing machine which includes
1. a screen adapted for use on a multihead screen printing machine
2. a test printing machine for determining the printing parameters for a silk screen
3. an electronic storage means on said silk screen adapted to receive and store said printing parameters
4. a screen printing machine which includes a central controller and/or print head controllers adapted to read and actuate said printing parameters stored on said silk screen when it is fitted to a print head.
The screen printing parameters to be stored may include
1. job number and customer identification
2. squeegee print speed,
3. squeegee flood speed
4. squeegee position limits
5. the ink colour
6. squeegee material to be used,
7. the screen tension when new
8. the number of print passes required,
9. accumulated total number of print passes
10. the optimum flash period for curing the ink
11. the print head on the machine to which the screen should be attached
The data storage on the silk screen is preferably able to be altered or updated by an operator when the screen is fitted to the production screen printing machine. The data can be transferred over a cable connection between the printing machines and the screen or by a wireless transmission which means the screen will also have a transmitter and receiver to facilitate access to the storage means. Alternatively the storage means can be a smart card which can receive a signal and transmit a reply powered by the received signal. The wireless transmission also makes it feasible to use a handheld programmer which can also key into the screen storage the printing parameters or updates to the parameters.
The actual storage device and the connection devices are preferably attached to the screen frame in a position that allows robust use of the screen.